This invention relates to a method for breaking a steel rod, a steel bar, or a steel pipe into billets for forging, rolling, etc., and more particularly to a method which yields billets such as forging billets with flat broken surfaces when relatively low mechanical loads are applied without causing large amounts of vibration or noise.
Forging billets are formed by cutting a steel rod or a steel pipe to given dimensions suitable for and preparatory to the forging operation. Steel rods, steel bars or steel pipes may be used as the starting material form and all will be defined herein as included in the term "steel rod", as referred to hereinafter. Hitherto, it has been common practice to obtain forging billets by either a shearing or a sawing technique.
The shearing technique has been more widely used than the sawing technique. However, shearing has a number of disadvantages, such as failure to achieve flat cut surfaces, deformation of the edge portions of the billets, and formation of burrs, cracks, etc., when hard steel rods made of bearing steel, high carbon alloy steel or high carbon steel are used as the base material. For these reasons, difficulties have been experienced in obtaining forging billets having precise and accurate weights. Die forging a billet of excessive weight results in a product having a surplus portion as flash, and wastes material. Also, in such instance, an overload is applied to the forging machine, so that a forging machine having a larger capacity is required to be used. When a forging billet of insufficient weight is used, a non-full sized or defective product necessarily results. In addition, the lack of flatness of the cut or sheared surface of a forging billet, during die forging in the axial direction of the billet, causes falling or inclination of the billet during forging with adverse effects and results on the product. The shearing technique of forming billets requires a very great shearing force, so that a costly shearing machine must be used with accompanying large amounts of vibration and noise during the shearing.
The sawing technique of forming billets yields satisfactory cut surfaces without causing excessive vibration and noise, but it suffers from poor work efficiency. In addition, in forming forging billets from steels of high hardness in a rolled state the rods must be subjected to annealing, thus increasing the cost.
To overcome the above briefly described defects, studies have been made of mechanical breaking of steel rods having notches therein. However, the mere application of a mechanical load on a notched rod fails to yield broken surfaces in alignment with the bottom of the notch, thus resulting in large variations in the weights of forging billets as well as poor flatness of the broken surfaces. The present invention is applicable not only to forging billets but also to billets for rolling, extruding, drawing, peeling and machining.